A shift register is used as a scan line driving circuit of a display device such as an organic electroluminescence (EL) display device. Such a shift register includes, as its output stage, a buffer amplifier having a large current supply capability to drive a scan line. It is required to suppress through-current in the buffer amplifier. In general, a buffer amplifier includes two transistors connected in series. The transistors are mutually exclusively in ON state. The through-current is a leakage current flowing through the transistors in OFF (non-conducting) state. Suppressing the through-current will reduce wasteful power consumption.
Recently, it has become common that a shift register is manufactured of a single type of transistors (for example, n-type transistors) to save manufacturing cost. Shift registers thus manufactured are likely to have a large through-current compared to CMOS shift registers. Because of this, suppression of through-current (and thus power consumption) is demanded all the more strongly.
There have been various techniques for conventional shift registers proposed to meet the demand (see Patent Literature (PTL) 1). In PTL 1, a shift register includes cascaded unit circuits each including two buffer amplifiers connected in parallel as an output stage as shown in FIG. 13. One of the buffer amplifiers outputs a driving signal to a corresponding scan line, and the other outputs a signal to the next unit circuit. An output stage in a unit circuit is thus separated into two buffer amplifiers in order to suppress through-current caused by bluntness of a driving signal output to a load (a scan line having stray capacitance).